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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 23 February 2011 by dana1981

In this post we continue our Prudent Path Week theme, and the examination of the two documents the "skeptics" referenced in their recent letter to Congress — 'Carbon Dioxide and Earth's Future: Pursuing the Prudent Path' and the NIPCC report. Specifically, we examine a major contradiction between the two reports regarding a key factor in climate science - climate sensitivity.

Medieval vs. Current Global Temperature

In their Prudent Path document, Craig and Sherwood Idso argue that the Medieval Warm Period (MWP) was at least as hot as today.

"it was just as warm as, or even warmer than, it has been recently during both the Roman and Medieval Warm Periods"

Informal Idsos

The document spends several pages qualitatively discussing various temperature proxy data sets from various isolated geographic locations — one of the main pursuits of the Idsos' website co2science.org. The only response this endeavor warrants is the suggestion that if the Idsos would like to attempt to use this data to demonstrate that the MWP was hotter than today, they should perform a quantitative assessment — combine these proxies into either a northern hemisphere or global data set, estimate the average temperature, and submit their results to a peer-reviewed scientific journal. Over a dozen such millennial northern hemisphere reconstructions have been peer-reviewed, and all agree that current temperatures are hotter than during the MWP peak.

Ljungqvist (2010)

The document also relies fairly heavily on one such millennial northern hemisphere reconstruction — Ljungqvist (2010) — which the Idsos refer to as a "stellar effort". However, this reconstruction is not substantially different from the many other millennial northern hemisphere temperature reconstructions, as Ljungqvist himself states in his paper:

“Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. AD 300–800, despite significant differences in both data coverage and methodology.”

Contrary to the Idsos' claims in the Prudent Path document, Ljungqvist says the following when combining his proxy reconstruction with recent instrumental temperature data:

“Since AD 1990, though, average temperatures in the extra-tropical Northern Hemisphere exceed those of any other warm decades the last two millennia, even the peak of the Medieval Warm Period”

Indeed by plotting Ljungqvist's data along with Moberg et al. (2005), Mann et al. (2008), and the surface temperature record, we can confirm that the three reconstructions are very similar, and all show the peak of the MWP approximately 0.5°C cooler than today's temperatures (Figure 1).

Thus we can see that the Prudent Path document's own references do not support its claim that the MWP peak was as hot or hotter than today's temperatures. This is a good thing, because the larger past natural temperature changes were, the larger the climate sensitivity.

Skepticism Requires Low Climate Sensitivity

Climate sensitivity (the amount the planet's average surface temperature will warm given a certain energy imbalance, including feedbacks) is the key to global warming skepticism. The amount of warming at the Earth's surface depends on two factors — the size of the energy imbalance, and the climate sensitivity to that energy. However, the first factor (the energy imbalance caused by the increase in greenhouse gases) is a well-measured and well-known quantity.

Therefore, the only way to argue that humans aren’t driving global temperatures now, and temperature change over the next century won’t be potentially catastrophic in a business-as-usual scenario, is if climate sensitivity is low. "Skeptic" climate scientists like Lindzen, Spencer, and Christy realize this, and it's why their arguments consistently center around the argument "climate sensitivity is low".

The heat trapped by the increased atmospheric CO2 has to go somewhere, and the only way it's not causing and will not cause significant global warming and climate change in the future is if it's suppressed by cooling effects from negative feedbacks. If this were the case, climate sensitivity would be low. And this is indeed a key argument made in the NIPCC report:

"Scientific research suggests the model-derived temperature sensitivity of the earth accepted by the IPCC is too large. Corrected feedbacks in the climate system could reduce climate sensitivity to values that are an order of magnitude smaller."

The NIPCC report is claiming that the IPCC sensitivity range is too high by a factor of 10, but the Idso Prudent Path document, by claiming that the MWP was as hot or hotter than today, is arguing that the IPCC sensitivity range is too low.

Hot MWP Means High Sensitivity

As John Cook has previously discussed, arguing for large swings in natural temperature variation such as a particularly hot MWP is akin to arguing for high climate sensitivity. Several scientific studies have examined the radiative forcings and temperature changes over the past millennium, such as Hegerl et al 2006, as shown in Figure 2:

Figure 2: Climate sensitivity from palaeoreconstructions going back 750 years, combined with climate sensitivity calculated from instrumental records. The horizontal bars represent the 5 to 95% range, indicating a climate sensitivity range of 1.5 to 6.2°C for a doubling of atmospheric CO2 (Hegerl et al 2006).

When you combine the temperature record over the past millennium with climate forcings, you get a most likely climate sensitivity value close to 3°C, consistent with the IPCC climate sensitivity range of 2°C to 4.5°C. So if the temperature swings were actually larger than in the reconstructions used by Hegerl and other studies on millennial climate sensitivity, it means the climate sensitivity is actually higher than the IPCC has concluded.

The two documents referenced in the "skeptic" letter to Congress blatantly contradict each other on this issue. The NIPCC report argues that the climate sensitivity is an order of magnitude lower than the IPCC range, while the Idso Prudent Path document indirectly argues that the sensitivity is higher than the IPCC range. On the most important issue for climate "skeptics" — climate sensitivity — the two documents cited in the "skeptic" letter to Congress contradict each other by a factor of ten.

The True Prudent Path

Ironically, although the two "skeptic" documents differ on the climate sensitivity parameter by an order of magnitude, both are wrong. There are many independent lines of evidence behind the IPCC climate sensitivity range, meaning that it's exceptionally unlikely that it's wrong by an order of magnitude, as the NIPCC report claims. And as discussed above, the evidence does not support the Idso claim that the MWP peak was as hot or hotter than today.

Thus the real "prudent path" involves proceeding under the assumption that the well-supported IPCC likely range of climate sensitivity (2 to 4.5°C with a most likely value of 3°C warming for a doubling of atmospheric CO2) is correct. In this scenario, we are heading towards extremely dangerous and potentially catastrophic warming and climate change this century in a business-as-usual scenario.

Thus the true prudent path involves taking immediate action to significantly reduce human CO2 emissions. If the "skeptics" want to convince us otherwise, they need to start by getting their story straight.

Comments

Dana, good work. I was dumbfounded when I looked at page 10 of the Prudent path document-- they did not include the temperature data from the observational record-- that is totally misleading, because the end date for the Ljungqvist reconstruction was around 1990. Is that end date correct?

Thanis Albatross. Ljungqvist extended his proxy reconstruction through the decade of 1990-1999. Half of his proxies (15) extend through 1989, and one-third (10) through 1999. But he also plots the instrumental temperature record, unlike the Idsos. Which, considering the relatively low number of proxies extending to the late 20th Century, is a smart thing to do.

Actually a warmer MWP would mean a climate sensitive to something other than CO2 and other greenhouse gases. The alleged 0.5 degrees cooler MWP even if true, +which I doubt) nothing points to a rapidly warming planet leading to forseeable dangers from CO2 emissions.

Climate sensitivity gives the temperature to any climate forcing, whether man-made (e.g. CO2) or natural (e.g. the sun). It differs relatively little for different forcings, as exemplified by a factor called "efficacy" (http://pubs.giss.nasa.gov/docs/2005/2005_Hansen_etal_2.pdf)

And don't forget that CO2 also has natural sources and is strongly implicated in climate changes in the history of the earth (see e.g. Richard Alley's AGU 2008 talk).

Bart Verheggen@4
I want to make sure I understand the argument correctly so bear with me.

If climate sensitivity were low (skeptic view) then based on what we know of the forcings at the time the temp would have been lower. Either sensitivity is higher than they claim or some other undefined/unknown force was at work in the MWP. I feel as though I am still missing something.

If you look at the graph in figure 1, it clearly shows that the highest point, which is the Moberg et al (2005) reconstruction is a full 0.5 deg. below current instrumental records. I don't understand why you would say "alleged if true". Its factual data right in front of your eyes.

Chemist - as Bart suggested, please do some research on forcing efficacies. I discussed the subject previously here.

pbjamm - you understand the argument correctly. If the MWP were hotter, it would mean the climate is more sensitive to a given radiative forcing, which would mean that it's also more sensitive to CO2. If sensitivity is low, either the MWP, LIA, Roman Warm Period, etc. must all have some additional unknown cause, or they must not have been very warm/cold.

RickG - not only did Chemist use the term "alleged" but he also said "which I doubt", despite the data presented in the article. One has to wonder what more it would take to erase Chemist's "doubt".

Taking the Moberg et al graph at face value, it took nearly 800 years to change from MWP peak to LIA low, a deltaT of approx 0.8 degrees C. That's 0.01 degrees per decade. The prior warming was ~0.5 degrees in 400 years or 0.013 degrees per decade. Now we are on a global trend of 0.15 degrees per decade, more than 10x the rate of these so-called natural variations - with trends of 0.3 deg/decade in the northern hemisphere extra-tropics.

What part of that doesn't point to rapid warming? If you take issue with this temperature reconstruction, we have several prior threads on the MWP/LIA and other use of proxies; I suggest you review all sources of data prior to dismissing this out-of-hand.

Yes, I think that's right. The way to get out of the explanation as e.g. given by Dana (#7) is indeed to climate that a) an hitherto undefined/unknown climate forcing was at work besides the known ones or b) the responsde to a known climate forcing is enhanced (e.g. the response to solar variations being enhanced by cosmic rays).

I think both arguments (a and b) are rather weak and unsubstantiated though, esp when taking into account multiple periods from the earth's past.

Just what we need, another ill-constructed hocky stick. Since the Ljundqvist paper used the Cru-tem and Had-crut data for recent temperatures that should be shown, not GISS. The GISS temperatures have established that they are high compared to other estimates, apparently because they use a few limited polar measurements to "fill in" data for the arctic circle.

You'll note that Moberg etal. and Ljungqvist both show the yr2000 temps at a O-.2 deg. anomaly. The spaghetti graph is good at hiding things. The only surprising data in the set is the GISS record and the question is why it suddenly departs from the other temperatures post 2000.

Chemist1 @3 & Bart Verheggen @4, Climate sensitivity is normally treated as being the same for all forcings. Obviously that is only an approximation. Because different forcings have different patterns of geographical and temporal effects, logically they will also have slight differences in feed backs.

As one example of this, an increased concentration of CO2 will preferentially warm high latitudes relative to low latitudes. The obvious consequence of this is that CO2 forcing will result in a stronger ice albedo feedback for a given level of mean global temperature rise.

In like manner, increased insolation preferentially warms the tropics. As a result they should have a stronger water vapour feed back and upper tropospheric hot spot than would be expected for a positive CO2 forcing.

However, this difference in feedbacks is likely to make only a small difference to climate sensitivity, so that equal climate sensitivity for all forcings is a valid approximation.

Indeed, General Circulation Models do not even make that approximation. Because they determine the effects of forcings cell by cell, the diferential effects of warming on feedbacks at different locations and altitudes is already incorporated into their design. That the output of GCMs is so consistent with approximately equal feedback is very strong support for the intuitive hypothesis of near equality of sensitivity for all feedbacks.

And to avoid the strawman, I said "strong support", not "evidence". The outputs of GCMs are just probabilistic predictions based on well known physical laws. Unless a major error in those predictions can be shown (ie, that predictions of all GCMs are artifacts rather than consequences of the laws they encode), then it is the very strong empirical support of of those physical laws that supports the near equality of sensitivities.

(I apologize for the "lecturing tone", it is an unfortunate consequence of writing for both clarity and accuracy. I am not setting myself up as an authority.)

Ah yes, Phil C, the old "GISS is unreliable schtick". For the record, GISS uses far more weather stations to compile it's data than HadCru does-especially around the Arctic regions-& so HadCru is getting a slightly shallower warming trend than RSS (Satellite) & GISS (ground-based). In truth, though, its the UAH trend that is the "odd-one-out", because of a failure to account for Diurnal Drift in the calculation of temperatures.

That shows approximately a 0.27 degree rise from 1979 to 2008 in global mean temperature, which as you know was anomalously cold for the 21st century. A better comparison is with Northern Hemisphere temperatures, which Moberg et al reconstructed. HadCRUt3nh shows nearly 0.5 degrees increase over 1976 for 2008, again an anomalously cold year.

For comparison, the MWP in Moberg et al averages around 1970 temperatures or lower, although just four years (1016, 1017, 1105 and 1106) rise to near 2008 levels, with the highest (1105 at 0.3717) being 0.43 degrees warmer than 1979, and hence cooler than the, cool for the 21st century, 2008 in the NH.

In this case, it is you who are trying to hide things on the spaghetti graph.

With regard to GISS temperatures, you are again wrong. First, deniers often claim that the GISS reconstruction of temperatures in the arctic circle are based on only a very few stations because only a very few such stations lie within the arctic circle itself. This deliberately - deceitfully - ignores the significant number of stations lying just outside the arctic circle but well within the range of the arctic circle for GISS's temperature reconstruction.

However, evidence does suggest that there is a problem with the GISS temperature reconstruction. Comparison with the DMI arctic temperature reconstruction shows that the use of stations outside the arctic circle to help reconstruct temperatures within in it has resulted in GISStemp underestimating the warming trend in the arctic by about 0.2 degrees per decade.

What looks like a hockey stick is Mann et al 1998 (you can also see from table 2 in the Ljungqvist PDF that Mann 2003 also fails to capture this variability)

So can we just nail this. The reconstructions that were so critically used by the IPCC are these earlier Mann reconstructions and if you are now accepting Fig1 as the correct reconstructions then it looks like the critics were right to highlight this problem. So would you be supportive of ClimateAudits attempts to highlight this problem early on?

Ah HR, I see you Denialists are still dwelling in 1998. Guess what, those of us who live in 2011 know that Mann was already held to account by no lesser body than the National Academy of Sciences. There, he accepted his error & went back & corrected his original work & re-submitted it for publication. There are about half a dozen other climate reconstructions that agree with the revised Mann reconstruction &-guess what-they all come out with peaks *cooler* than the current 30-year period.

All of this is a typical denialist straw-man. Errors can be made in *all* branches of science-even climatology-but there are already processes in place to correct them. We certainly don't need the Denialists pushing the issue just to advance their own agenda.

I don't understand the problem you are referring to. Figure 1 covers a period twice as long as the original Mann 98 record, so it's not surprising that the figures look different from one another. If you compare results from the same time interval, beginning in 1000, then the results in Figure 1 seem to be very similar to those from Mann.

We have philc rejecting Moberg, Ljungqvist and GISSTemp here, with Chemist doing the same here. HR, of course, misses the point entirely, choosing to focus on the old hockey stick (an outdated MWP graph) rather than the business end of the hockey stick (most goals are scored when the puck leaves the blade, not the shaft).

Are these folks actually saying that not only is there no way to form any reconstruction of past temperatures, but even current temperature measurements are suspect? Does anyone really believe that we do not even know enough to measure temperature? Or how temperature variation impacts things like tree ring growth and other proxies? That there is no valid science behind any of these reconstructions? If so, all such measures are invalid -- and how can they now insist that 'it warmed before' or 'it's not warming rapidly now'?

Denialism is choosing to deny reality as a way to avoid an uncomfortable truth: "[it] is the refusal to accept an empirically verifiable reality. It is an essentially irrational action that withholds validation of a historical experience or event".

Thanks Andy for that graph. I guess the big problem is 0.4oC or so extra variability seen in the blue curve than the red curve from 1000-1500. If as you suggest this level of difference in temp is not worth arguing over than why are we getting so excited by what's happening present day?

19 Marcus

Great Mann 1998 is junk science, that's good to know. Mann 2003 also?

And why is this important? Well from a glance at Hegerl 2000 (which should be Hegerl et al 2006 I think Dana) it looks like his results are being influenced by these early incorrect reconstructions.

HR @18, the real question here is why are you ignoring the push by deniers to retain an obsolete reconstruction based on a single temperature series in central England, plus (for the early periods) the estimates of one researcher? The preference for this obsolete graph is clearly stated by McKitrick, for example in "What is the 'Hockey Stick'debate about?" (April 2005), in which he reproduces that obsolete graph as Figure 3. If you missed that date, McKitrick was still pushing that obsolete graph two months after the publication of Moberg 2005. In view of that, it is disingenuous for deniers to now claim Moberg as confirmation of MacIntyre and McKitrick's views, rather than of Mann's.

It is very clear that Moberg 2005 matches much better with MBH 99 than with IPCC 1990, particularly during the MWP. MBH 99 clearly understates the LIA, although the extent to which they do may be exaggerated in this graph in that Moberg 2005 shows a much cooler LIA than most modern reconstructions.

So, it is clear that MBH 99 (and 98) are a major advance over IPCC 1990. Since then statistical techniques in reconstructions have improved so that there are several reconstructions that give better results than MBH 99, and are consequently preferred. Stuck in a time warp, deniers are still using IPCC 1990 and attacking MBH 98 as if that somehow undermines modern reconstructions.

As to M&M's particular criticisms of MBH 98, many of them are simply wrong, and the rest much over exaggerated in their effect on the reconstruction. I do not think it is good science to be merely political attack dogs trying to pick up any flaws on papers whose conclusions you dislike while giving a free pass to papers whose conclusions you do like. The complete hypocrisy of M&M is shown by the complete pass they give to IPCC 1990 compared to the fine tooth comb they run through MBH 98.

Excellent points muoncounter. I've learnt that no point in debating within anyone where their position is such that they can imagine no data that would change their mind. Do philc and chemist1 fit this? Perhaps we should ask.

Are the "skeptics" trying to see how many own goals they can score on this thread? Truly unbelievable.

HR, continues to miss the point and argue strawmen. It seems that he has not read the main post which has this quote from the Ljungqvist (2010):

"Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. AD 300–800, despite significant differences in both data coverage and methodology.”

And "skeptics" love the Ljungqvist reconstruction. How very inconvenient for them that it agrees well with Moberg and Mann, and shows that current N. Hemisphere land temps are warmer than those observe during the MWP.

Come on, Marcus never said that MBH98 was "junk science", neither did the NAS panel--now HR is grossly distorting and misrepresenting the facts.

And Hegerl and Knutti (2008) is the most recent meta analysis of estimates of climate sensitivity. Why do some people insist on being stuck in circa 2000?

No-so typical of a denialist to misrepresent the facts. Mann 98 was just plain science. You seem to not understand that paleo-climatology was still in its relative infancy when Mann started this work. Science is rarely letter perfect first time round (if ever), it usually needs an iteration or two (or even 3) to get it completely right. In this case, Mann relied too heavily on a single proxy to obtain his reconstructions-getting a *slightly* flatter temperature graph than what's been obtained in subsequent reconstructions. Given that Mann 2003 is much closer to the more than half a dozen reconstructions that currently exist suggests that he took the criticisms on board & extended his range of proxies the next time around. The point is that no matter what reconstruction you look at, the extent & rate of warming is *nothing* like what we've seen in the last 50 years-no matter what you & your denialist mates say. Yet instead of dealing with this uncomfortable fact, you'd rather create straw-men arguments that reveal a great deal more about your own ignorance of scientific processes than about the science itself.

"Mann 1998 is junk science" - Mann 1998 was first attempt - it would be better to describe it as superceded science. I would refer to "junk" as papers with serious logical flaws or methodologies that would be inappropriate for the time of publication.

HR 23, of course the 0.3 degree difference in variation between MBH and Moberg, and the 0.4 degree difference between MBH and Lundqvist is important. That is why climate scientists have not rested on their laurels and continue to refine the reconstructions.

What is puzzling is why deniers cannot recognize that the 0.5 difference between IPCC 1990 and Lundqvist. (Note, the variation of Lundqvist compared to MBH, IPCC 1990 and Moberg 2005 is greatly exagerated because of the higher resolution smoothing used.)

There are several graphs on this post showing between 0.8 and ~1.0 degrees of warming since circa 1910. Your statement suggests you believe all of them are wrong. Sounds like you're the one preaching 'no science'.

"You should really learn to construct an argument without resorting to offense."

I just tell it like I see it. If you take offense to being labeled for what you are & what you do, then the fault lies with you-not me. The IPCC then, as now, was relying on the best information to hand-namely Mann 98. As has already been pointed out to you (but you clearly choose to ignore) the IPCC, in 1990, was relying on an even more limited paleo-climate reconstruction using a proxy from central England. In spite of its imperfections, Mann was a considerable improvement on this, & the IPCC included it. The IPCC has since incorporated the much improved reconstructions that have come out more recently. So again, your arguments reveal more about your own lack of knowledge of the processes than anything about the IPCC.

"Once again fellow posters in general, I did my homework, and see that the data is not so factual or well evidenced... "

....and once again, we're expected to simply take your word for it, as you've failed to provide any *proof* of your statements. Seriously, you "skeptics" seem to expect others to take a lot on *faith*, don't you?

Muon, agian these early Mann recocstructions are there in the 2007 IPCC report. Sorry for the repetition but is it me or the IPCC that's stuck in the past? And if it's both then which is more important and which is the one you should be getting most agitated about?

Further to Marcus @27 and scaddenp @29, Lundqvist has this to say about the difference between his and Mann's reconstruction:

"Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005)and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. AD 300–800, despite significant differences in both data coverage and methodology."

My emphasis, obviously.

Unlike deniers around the world, it is note worthy that Lundqvist has noticed that Mann and the "hockey team" have moved on. Because they want actual reconstructions, not just political talking points, they have used better data and techniques as they have become available, so that now Mann et al (2008) actually shows the most variability of the three reconstructions (and Lundqvist the least).

Go here. Now AR4 was released in 2007, and the figure shown in the link shows 12 paleo reconstructions published between 1998 and 2006. MBH99 is in there, as is Moberg et al. (2005). Now AR5 will no doubt include Lungqvist (2010), as well as Mann et al. (2008, 2009) and any other recent reconstructions worth merit. This is really not difficult.

Again I have to wonder whether you actually took the time to read Dana's post. The reconstruction under discussion here, in this post, was Ljungqvist, which shows that recent N. Hemisphere land temps. are running higher than during the MWP. Yet you insist on arguing a strawman about earlier reconstructions, that really smacks of desperation.

Do you accept Ljungqvist (2010) as a reliable reconstruction? Other 'skeptics' do.

If you don't want people to think that you are in denial about AGW, stop behaving like someone who is in denial. Going by your posts on this thread it is becoming increasingly difficult to give you the benefit of the doubt.

Further to Muoncounter @40, the IPCC AR4 even discuss Lamb's reconstruction (the basis of IPCC 1990) in box 6.4

Because the IPCC is trying to advance understanding of the science, it clearly tries to show how we got from our prior state of understanding to our current state of understanding. It acknowledges the past without being stuck in it.

In constrast, M@M were still pushing a reconstruction made without using any statistical techniques in the 1960s (IPCC 1990) in 2005, and WUWT was still pushing it in 2010.

Several commenters here seem to be missing the point and taking the discussion off topic. The point is that we would be better off if the original hockey stick were correct. It would mean that, as the "skeptics" require, climate sensitivity might be low.

As reconstructions have progressed, yes, they now have less of a 'hockey stick' shape. That is a point against "skepticism". The "skeptics" seem so eager to score a point against Mann or the IPCC or whoever that they don't realize they're scoring major points against themselves. Hence the article title.

So if I talk about early Mann reconstructions I'm stuck in the past, If IPCC 2007 refers to early Mann reconstructions it's...... Ah yes I see your logic now.

40 muoncounter

Hey they dropped the early 1990 estimate why not drop Mann 1999? The National Academy of Science had already questioned the result in 2006. I understand science evolves, it really just a question why the IPCC was so slow to end it's love affair with early Mann.

"BTW, that's another figure showing at least 1 degree of warming since 1910." In the instrumental record not in paleo's, right?

"So can we just nail this. The reconstructions that were so critically used by the IPCC are these earlier Mann reconstructions and if you are now accepting Fig1 as the correct reconstructions then it looks like the critics were right to highlight this problem. So would you be supportive of ClimateAudits attempts to highlight this problem early on?"

The IPCC wrote (AR4):

"McIntyre and McKitrick (2003) reported that they were unable to replicate the results of Mann et al. (1998). Wahl and Ammann (2007) showed that this was a consequence of differences in the way McIntyre and McKitrick (2003) had implemented the method of Mann et al. (1998) and that the original reconstruction could be closely duplicated using the original proxy data. McIntyre and McKitrick (2005a,b) raised further concerns about the details of the Mann et al. (1998) method, principally relating to the independent verification of the reconstruction against 19th-century instrumental temperature data and to the extraction of the dominant modes of variability present in a network of western North American tree ring chronologies, using Principal Components Analysis. The latter may have some theoretical foundation, but Wahl and Amman (2006) also show that the impact on the amplitude of the final reconstruction is very small (~0.05°C; for further discussion of these issues see also Huybers, 2005; McIntyre and McKitrick, 2005c,d; von Storch and Zorita, 2005)."

So, of M&M's criticisms, one is based on an incorrect implementation. Further, even if methods are applied to the data which avoid the issue entirely, MBH's reconstruction still emerges from the data. And the other statistical issues raised by M&M only result in a 0.05 degree distortion of the result.

So, does HR really want to stand by Climate Audit's efforts to raise this mammoth problem of a potential 0.05 degree distortion in MBH's results?

Does he further want to stand by their insistence that IPCC 1990 better reflected reality?

Does he further want to stand by their "audit technique" that takes a potential distortion in a scientific graph of 0.05 degrees C to Congress, but ignores as irrelevant any potential flaws in IPCC 1990 (which is again reproduced without critical scrutiny in the Wegman report)? Does he want scientific scrutiny to be, like the practise of M&M, entirely based on whether they like or dislike the political consequences of the science?

If he does not want to stand by any of these, but instead wishes to withdraw his question @18 as ill conceived, well then perhaps he does not deserve the denier label.

HR @46, as previously indicated, they did include a discussion of Lamb, whose graph was included in IPCC 1990:

"Lamb (1965) seems to have been the first to coin the phrase ‘Medieval Warm Epoch’ or ‘Little Optimum’ to describe the totality of multiple strands of evidence principally drawn from western Europe, for a period of widespread and generally warmer temperatures which he put at between AD 1000 and 1200 (Lamb, 1982). It is important to note that Lamb also considered the warmest conditions to have occurred at different times in different areas: between 950 and 1200 in European Russia and Greenland, but somewhat later, between 1150 and 1300 (though with notable warmth also in the later 900s) in most of Europe (Lamb, 1977).

Much of the evidence used by Lamb was drawn from a very diverse mixture of sources such as historical information, evidence of treeline and vegetation changes, or records of the cultivation of cereals and vines. He also drew inferences from very preliminary analyses of some Greenland ice core data and European tree ring records. Much of this evidence was difficult to interpret in terms of accurate quantitative temperature influences. Much was not precisely dated, representing physical or biological systems that involve complex lags between forcing and response, as is the case for vegetation and glacier changes. Lamb’s analyses also predate any formal statistical calibration of much of the evidence he considered. He concluded that ‘High Medieval’ temperatures were probably 1.0°C to 2.0°C above early 20th-century levels at various European locations (Lamb, 1977; Bradley et al., 2003a)."

It was not appropriate to include it on the spaghetti graph because (for the highlighted reasons) it was not a comparable reconstruction.

"o if I talk about early Mann reconstructions I'm stuck in the past, If IPCC 2007 refers to early Mann reconstructions it's...... Ah yes I see your logic now."

I dont think so. Can you see the difference between presenting an old reconstruction as if it was the current state of "AGW thinking" (the pseudo-skeptic tactic discussed), and presenting a history of reconstructions showing the effect of different proxies and methodologies leading to a convergence of evidence? You might also like to read the accompanying text to see if IPCC is "stuck in the past".